Gaseous discharge device and electrode assembly for use therein



7 Feb. 10, 1942. c STOCKER 2,272,486

GASEQUS DISCHARGE DEVICE AND ELECTRODE ASSEMBLY FOR- USE THEREIN FiledApril 10, 1959 67050101725106?! INVENTOR.

ATTORNEY.

Patented Feb. 10,1942

GASEOUS DISCHARGE DEVICE AND ELEC- TBODE ASSEMBLY FOR USE THEREIN IClosman P. Stocker, Lorain, Ohio, assignor, by

direct and mesnc assignments, to General Electric Company, a corporationof New York Application April 10, 1939, Serial No. 266,971

11 Claims.

This invention relates to gaseous electric discharge devices generallyand more particularly to such devices having electrode assemblies whichmake use of filaments and auxiliary electrodes.

Typical low voltage gaseous discharge lamps usually contain mixtures ofmonatomic or diatomic gases,.or mixtures of both, together with thevapor of some metal such as sodium, mercury, etc. These lamps operate on110 volts and 220 volts and are usually provided with a fluorescentcoating on the inside of the glass envelope so that the main gaseouselectric discharge causes visible light to be emitted from the lamp.Such lamps are equipped with filaments coated with some electronemitting material such as barium, thorium, etc. During the startingoperation the filaments are heated by current flow through thefilaments, under which condition they emit electrons copiously. When thelamp ignites, the filaments are tie-energized and the main gaseouselectric discharge occurs between the two coated filaments which act asmain electrodes. ,The main discharge produces a hot spot on the coatedfilaments which permits the lamp to be operated from the source of lowvoltage electric current.

In the low voltage electric discharge lamps, such lamps are equippedwith filaments which require more current for heating the filament thanis required by the main discharge are when the lamp is in operation. Forexample, a com--. mercially available 20-watt fluorescent lamp requires.5 ampere for filament heating and the normal discharge are currentthrough the lamp is .35 ampere.

In my copending U. S. patent application Serial No. 265,645, filed April3, 1939, I show, de-

scribe and claim a low voltage electric discharge lamp starting circuitwhich depends for its operation upon the design of the gaseous electricdischarge lamp so that the main discharge current is higher than thecurrent required through the filament for' the starting condition. Sinceit is necessary to make such a lamp with a filament of fine wire, it isdesirable to transfer the main discharge are from the filament to someelectrode able to withstand the heavy discharge current.

My present invention provides for protecting the small starting filamentduring normal operation of the lamp. To accomplish this I make voltageelectric discharge lamp in which the starting current is appreciablyless than the operating current.

Another object of my invention is to provide a main electrode assemblyin a low voltage gaseous discharge lamp, which main electrode assemblyhas two coated auxiliary electrodes shunted by a starting filament.

An object of my invention is to provide an electric discharge lamphaving a starting fila ment, which is protected from the main aredischarge of the lamp by means of a coated auxiliary electrode.

Another object of my invention is to provide an electric discharge lamphaving two main electrodes, each main electrode utilizing a plurality ofelements coated with electron emitting material and a filament.

Another object of my invention is to provide a main electrode assembly,comprising a plurality of coated elements and a filament covered .by asleeve of material adapted to emit electrons when heated.

. Another object of my invention is to provide 'for causing a. localdischarge to occur between parts of at least one of the main electrodesof a gaseous. discharge device.

Another object of my invention is to cause an auxiliary arc to by-passthe current around the filament during starting.

Another object of my invention is to cause electric discharge lamps,equipped with filaments, to'

operate in the following sequence:

a; Heat filaments.

b. Cause auxiliary discharge.

0. Maintain potential difference between main electrodes, sufficient toignite electric discharge lamp.

d. Limit current in main discharge path to de- Other objects andfeatures of my invention, the novel features of which are particularlypointed out in the claims appended hereto, may be more readily and morefully understood from the following description when read with referenceto the accompanying drawing, in which like parts of my invention aredesignated by like reference characters and in which:

Figure 1 shows in detail the construction of an electrode assemblyhaving a filament and two auxiliary coated electrodes all of whichcomprise a single main electrode.

Figure 2 shows an electric gaseous discharge lamp equipped with two mainelectrodes and connected in circuit relation for operation from a sourceof alternating current.

Figure 3 is a detailed drawing in which a main electrode assembly havingtwo auxiliary electrodes shunted by a filament, the filament beingprotected by two coated electron emitting covers, each coverelectrically connected to a difierent auxiliary electrode. V

Figure 4 shows the construction of a main electrode assembly comprisingone auxiliary electrode together with a filament with protectivecovering.

In the preferred embodiment of my electrode assembly shown in Figure 1,I provided two auxiliary electrodes I6 and II which may be made of wireand formed in a spiral. The auxiliary electrodes are coated with bariumoxide or strontium oxide, or any other suitable electron emittingmateriall Filament I4 shunts auxiliary electrodes I6 and I1. Electronemitting sleeve 32 covers filament I4. Sleeve 32 is connected toauxiliary electrode II by lead 28.

With reference to Figure 2, lamp I 3 is equipped with two main electrodeassemblies. Each main electrode assembly comprises two coated auxiliaryelectrodes shunted by a filament. saturable inductance I2 is connectedin series with filaments I4 and I5 and in parallel with lamp I3. Sourceof alternating current III is connected through current limitinginductance II to the unused filament terminals 23 and 25 on lamp I3.

To start lamp I3, current flows from source of alternating current IIJthrough linear inductance II, filament I4, saturable inductance I2,filament I5 and back to the source of alternating current I 0. Underthis condition and before the main discharge occurs between the spacedmain electrodes, saturable inductance I2 saturates and passes suificientcurrent to heat filaments I4 and I5. Filaments I4 and I5 heat theelectronemitting material which is shown as sleeves 32 and 33. Underthis condition the voltage drop across filaments I4 and I5 is suflicientto cause an auxiliary arc discharge to occur between the auxiliaryelectrodes I6 and I1 and I8 and I9. These auxiliary discharges may occurthrough gaps 20 and 2I respectively and shunt filaments I4 and I5. Theshunting action of the auxiliary arc is to bypass excessive currentaround the filament. In my invention the auxiliary arc dischargefunctions to condition lamp I3 for starting but it also serves toprotect the filament from burn-out in case of slightly excessivecurrents. The auxiliary discharge, together with energy from theassociated filaments, heats the coated auxiliary electrodes I6 and I1and I8 and I9 and conditions the lamp for starting. It is to-beunderstood that the discharge lamp contains a gaseous atmosphere capableof conducting electric current when excited by an electric dischargebetween the main electrode assemblies.

Due to the fact that the voltage sustained by saturable inductance I2 ishigher than the voltage required for the ignition of lamp I3, duringstarting condition, a main discharge will occur from a part or acombination of parts of one main electrode to a part or a combination ofparts of the other main electrode. Upon ignition of lamp I3, the voltageacross saturable inductance I2 is decreased and saturable inductance I2is operated at a lower flux density which causes the impedance ofinductance I2 to increase greatly. Thisjncrease in impedance reduces theheating in filaments I4 and I5 and permits the main arc discharge tooccur between the main electrode assemblies. As shown in Figure 2, forexample, the main discharge may occur between a hot spot on auxiliaryelectrode II and a hot spot on auxiliary electrode I8.

I consider the lamp I3 shown in Figure 2 as having two spaced mainelectrodes and each main .electrode having spaced parts shunted by afilament.

I prefer to have the auxiliary electrodes made from wire or thin metalso that the heat, clue to the main electric discharge will not beconducted away too rapidly. To function properly, the auxiliaryelectrodes should be capable of maintaining a hot spot which aids incausing the electron emitting material to maintain a supply ofelectrons. In Figure 1, auxiliary electrodes I6 and II are shown in theform of a spiral wire which contains the coating of material capable ofsupplying electrons. Many modifications of the auxiliary electrodes arepossible, but it should be kept in mind that they should be capable ofmaintaining a hot spot when subjected to the main arc discharge of thelamp. The auxiliary electrodes are designed to be heated by the maindischarge are and since they are coated with'an electron emittingmaterial, they relieve the starting filaments I4 and I5from the fullheat of the main discharge during normal operation of the lamp. Also,due to the fact that auxiliary electrodes I6 and II and auxiliaryelectrodes I3 and I9 are coated, the auxiliary discharge arcs throughgaps 20 and 2| are more easily started and the lamp is more .easilyconditioned for starting.

In the construction of the main electrode shown in Figure 1, I prefer tohave the filament covered with a sleeve 32 of electron emittingmaterial. This sleeve 32 is connected to one auxiliary electrode by lead28. It is therefore possible for the main arc discharge to occur fromelectron emitting sleeve 32 or from auxiliary electrodes I6 and II, orfrom a combination of these elements. When sleeve 32 is used, I preferto omit the electron emitting material from filament I4. Sleeve 32 isused to protect filament I4 fromthe main electric discharge should thisdischarge localize upon some part of sleeve 32. Normally, however, themain electric discharge will occur from one of the auxiliary electrodes,that is, electrodes I6 or II.

Figure 3 shows a modification of my invention in which the electronemitting sleeve is split into two parts designated 30 and 3|. Sleeve 30is connected to auxiliary electrode 21 by, lead 28 and sleeve 3| isconnected to auxiliary electrode 26 by lead 29. This constructionpermits electron emitting sleeves 3ll and 3| to be maintained atpotentials which are determined by the potential of the auxiliaryelectrodes to which they are attached. This means that an electricdischarge lamp may be connected to a starting circuit and there willalways be one auxiliary electrode and an associated electron emittingsleeve maintained at a high potential with respect to the otherauxiliary electrode and electron emitting sleeve associated therewith inthe same electrode assembly.

Figure 4 shows a construction of a main electrode in which one auxiliaryelectrode I6 is used and in which the other auxiliary electrode is theelectron emitting sleeve 32 which covers filament II. In this particularconstruction auxiliary discharges for starting purposes are providedbe-- It will be noted that electron filament I4 is available to producethe auxiliary discharge arc through gap 20. In normal operation anelectric gaseous discharge lamp equipped with two main electrodeassemblies as shown in Figure- 4 operates in a manner similar to thatdescribed in connection with Figure 2. In this case when the filamentheat is reduced after ignition takes place the main arc discharge willoccur between auxiliary electrode It or electron emitting sleeve 32 orcombinations of these elements.

While I have described my invention with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and scope of the inventionas hereinafter claimed.

I claim as my invention:

1. An electrode assembly for use in a gaseous electric discharge lamp,comprising in combination, a filament; an electron emitting sleevecovering said filament, and at least one auxiliary electrode coated withelectron emitting material electrically connected to one side of saidfilament, said electron emitting sleeve being connected to the oppositeside of said filament and being interposed between said filament andsaid auxiliary v electrode.

2. An electrode assembly for use in a low voltage gaseous electricdischarge lamp, comprising a filament, an electron emitting sleevecovering the filament, two auxiliary electrodes coated with electronemitting material, said electron emitting sleeve being connected to oneside of said filament, and said filament connected in shunt relationwith said auxiliary electrodes.

3. A gaseous electric discharge lamp comprising, a container, mainelectrodes sealed therein, a gaseous atmosphere capable of conductingelectric current when excited by an electric discharge between said mainelectrodes, said main electrodes each comprising two auxiliaryelectrodes coated with electron emitting material; shunted by anotherelectrode coated with electron-emitting material and located behind saidauxiliary electrodes.

between said lead-in wires, said electron emitting sleeve beinginterposed between said filament and said auxiliary electrode andconnected to one lead-in wire and said auxiliary electrode bei connectedto the other said lead-in wire.

6. In a low voltage electric discharge lamp having activated startingelectrodes in which the current through the electrodes during startingis substantially less than the current taken by the electric dischargelamp in normal operation, an electrode assembly comprising. twoauxiliary electrodes coated with electron emitting material, a startingelectrode also coated with electronemitting material and shunting saidelectrodes and located behind said auxiliary electrodes, said startingelectrode having sufilcient drop across it to cause an auxiliarydischarge are between said auxiliary electrodes during the startingcondition.

7. A low voltage gaseous electric discharge lamp having two mainelectrode assemblies sealed therein, comprising a container, a gaseousatmosphere capable of conducting electric current when excited by anelectric discharge between said main electrode assembly, said mainelectrode assembly being substantially as claimed in claim 1.

8. The method of operating a gaseous electric discharge device havingspaced main electrodes in which the main spaced electrodes have spacedparts comprising, the steps of applying a preheating current to aportionof at least one of the spaced main electrodes, producing a localdischarge between the spaced parts of said one of the spaced mainelectrodes, and impressing a voltage across the main electrodes to causea discharge current to' occur between the main electrodes, saiddischarge current between said main electrodes being substantiallygreater than said preheating current.

' 9. An electrode assembly for use in a gaseous electric discharge lamp,comprising in combination, a filament, at least one auxiliary electrodecoated with electron emitting material electrically connected to oneside of said filament, an electron emitting shield having a portionspaced between the filament and said one auxiliary electrode, saidcovering different portions of said filament. and

at least one coated auxiliary electrode electrically connected to oneside of said filament, means for connecting said electron emittingshields to opposite sides of said filament.

CLOSMAN P. srocxna'.

